1. Field of the Invention
The present invention relates to a system and method for spinal fixation, stabilization and/or fusion of the human occipito-cervical junction. Additionally, the invention is further directed to an apparatus and method for the treatment of an abnormal neuraxial angle, abnormal clivo-axial angle and mitigation of neurological conditions underlying neurobehavioral disorders arising as a result of abnormalities of the neuraxial angle, clivo-axial angle, skull base, craniocervical, posterior fossa and combinations thereof, which, without wishing to be bound by theory in a subset of individuals, cause neuro-behavioral disorders such as autism, autism spectrum of disorders, bipolar disorder and other neurological disorders. The present invention is directed to the treatment of these neurological disorders through the recognition, diagnosis, and normalization of the craniospinal relationship by fixation, stabilization and/or fusion of the human occipito-cervical junction.
2. Description of the Related Technology
The normal range of motion of the craniospinal junction includes about 27° of flexion and extension, and 90° of lateral rotation; the craniospinal junction is thus the most mobile and articulating part of the human body. It is also the most active part of the human body in movement throughout the day, typically performing greater than 3 million motions a year. Because the craniospinal junction transmits the entire nervous structure to the body (with the exception of the vagus nerve), and is thus unfortunately susceptible to a host of degenerative disorders that can cause cranio-cervical instability. Common causes of cranio-cervical instability, include traumatic fractures, which account for approximately 3,000 fractures of the upper spine related to head trauma each year; congenital diseases, such as Ehlers Danlos syndrome, Down's syndrome, Morquio's syndrome and spondyloepiphyseal dysplasia syndrome, with a prevalence of at least 50,000; and osteogenesis imperfecta, with a prevalence of 7,000 patients. Additionally there are numerous causes of bone softening related to malabsorption syndromes and other renal/metabolic and endocrine syndromes that result in abnormal craniospinal relationships. Cancer and infections that involve the craniocervical junction can also cause destruction of the stabilizing elements.
Surgical intervention is often necessary to stabilize the craniocervical junction, restore neurologic function and prevent further neurologic deterioration. Hitherto, patients undergoing craniospinal stabilization have required an extensive surgical correction. Some patients undergo decompressive surgery from the front of the neck (transoral resection of the uppermost part of the spine), followed by fusion in the back of the neck and 3 months of stabilization in a halo brace, which encompasses the head (held by 4 screws in the skull) and the upper body. Other traditional fixation devices and methods are described in U.S. Pat. Nos. 5,030,220; 5,034,011; 5,545,164; 5,507,745; 6,547,790; 6,524,315 and 6,902,565 B2 as well as U.S. Published Patent Applications US2005/0288669 A1, US2005/0283153 A1 and US2005/0080417 A1.
These conventional fixation systems and methods, however, are not suitable for circumstances wherein problems arise due to poor bone quality or bone defects, such as an inadequate amount of bone to which a fixation system may be anchored. For example, approximately 70,000 suboccipital craniotomies have been preformed for Chiari malformation, of which about half require revision involving the reduction of the clivo-axial angle and fusion stabilization. Traditional fixation and cranial attachment devices are unsuitable in these circumstances in view of the limited amount of remaining bone, the width of the craniotomy defect or the thinness of the overlying scalp toward the midline. Furthermore the width and height of the cranial defect does not leave enough space to fasten a device below the transverse sinus of the calvarium. Therefore, there exists a need for an improved system and methodology that enables craniospinal stabilization in patients suffering from poor bone quality and bone defects.